1. The Field of the Invention
The field of this invention relates to windshield wiper assemblies and, more particularly, to novel heat conducting apparatus for wiper blades.
2. The Background Art
Wiper arm assemblies, in general, are responsible for clearing and removing precipitation, dirt and other forms of debris which accumulate on the exterior surface of windshields and rear windows of motor vehicles. Typically, wiper arm assemblies operate by reciprocating at least one wiper blade back and forth across the windshield to provide a clean and clear visual field for the driver and occupants of the vehicle. During ambient freezing conditions, however, significant complications may arise having adverse effects on the functionality of wiper arm assemblies.
For example, in cold inclement weather, precipitation in the form of snow and ice may accumulate on the surface of a windshield and impair general visibility therethrough. As snow and ice begins to collect on wiper arm assemblies, wiper blades typically begin to harden, thus losing their flexibility. Consequently, this loss of flexibility in a wiper blade generally results in a notable interference in the efficiency of the clearing action of the blade.
Solid formations of ice may develop between wiper blades and the surface of the windshield causing the wiper blade to freeze to the windshield, thereby restricting subsequent reciprocating movement of the wiper blades across the surface of the windshield for clearing a visual field for the driver and occupants of the vehicle. Similarly, wiper blades may become so encrusted with snow and ice that solid formations of ice develop on the leading edges of the wiper blades causing the blades to become physically lifted and removed from direct contact with the surface of the glass. When this happens, the ability of the wiper blade to effectively track the contour of the windshield is seriously frustrated. In addition, under these circumstances, as the wiper arm assembly passes the wiper blade back and forth across the windshield, the ice formed on the leading edge of the blade typically produces streaks and smears of slush or water across the surface of the windshield resulting in subsequent visual obstructions to the driver and occupants of the vehicle.
In an effort to soften and melt accumulations of snow and ice on a windshield, window defrosters were developed by those skilled in the art. Traditionally, prior art defrosters were developed to generate circulating currents of warm air which are directed against the interior surface of the windshield or window. The amount of heat generated by prior art defrosters, however, is generally insufficient to melt solid formations of ice or snow which have accumulated on wiper blades or wiper arm assemblies. Moreover, window defrosters of the prior art are typically unable to transfer sufficient heat to soften the stiffness of a wiper blade which has lost its flexibility and initially hardened due to ambient freezing conditions. In some instances, prior art windshield defrosters begin to thaw accumulations of snow and ice formed on upper surfaces of the windshield, thereby creating a watery slush which typically runs down the surface of the windshield and begins to freeze on the wiping edge of the wiper blade, thereby constructively immobilizing the effectiveness of the clearing action of the wiper blade.
In an attempt to overcome these disadvantages, those skilled in the art developed various wiper blade heating assemblies which provide heat directly to the body of the wiper blade in an effort to remove and further prevent accumulations of snow and/or ice forming thereon. These attempts, however, have generally proven to be very costly and substantially ineffective.
For example, prior art wiper blade heating assemblies were developed by those skilled in the art utilizing extremely expensive resistive materials, such as, Nichrome and tungsten, as heat conductive elements. The excessive cost of Nichrome and tungsten when used as heating elements may be considered nominal when their uses are essential to sustain high heat outputs typically in excess of 523.degree. C. (1000.degree. F.). However, when considerably less heat is required to melt snow and/or ice accumulations from windshields, wiper blades or wiper blade assemblies, the cost of Nichrome or tungsten is generally considered prohibitive from a manufacturing viewpoint. Pursuant thereto, the cost of utilizing Nichrome or tungsten as heating elements in prior art wiper blade heating assemblies typically raises the market price of the heating assembly to a point that it may become an unaffordable solution for the consumer. As will be appreciated in this art, economic considerations of this nature are significant when dealing with the highly competitive automobile industry, since relatively complicated devices are frequently found to be commercially impractical. Accordingly, even a slight savings in cost may substantially enhance the commercial appeal of a particular component or assembly when considering issues of mass production of the product.
A major disadvantage with wiper blade heating assemblies of the prior art is their use of heating elements which typically require a protective coating of insulation to shield the elastomeric, rubber-like characteristics of the wiper blade from the direct heat output generated by the heating element. Types of protective insulations typically used to encase prior art heating elements, include for example, ceramic, teflon, nylon polymer coatings, etc., all of which generally interfere with the overall flexibility of the wiper blade. As a result, prior art wiper blades having heating elements embedded therein or in connection therewith, typically forfeit a significant portion of their resiliency as a result of the non-flexible characteristics of the insulated coatings surrounding the heating elements. Moreover, in this regard, prior art heating elements generally restrict the ability of the blade to track the contour of the windshield with precision.
In an effort to address the disadvantages associated with the lack of flexibility in wiper blades of prior art wiper blade heating assemblies, those skilled in the art developed a method for vulcanizing wiper blades comprising a mixture of carbon black and graphite to form a conductive wiper blade. This prior art process for vulcanizing rubber, however, requires high concentrations of carbon black to induce sufficient conductivity in the wiper blade having a negative effect on decreasing the flexibility of the blade and increasing the hardness of the rubber so that the wiper blade is no longer suitable for tracking the contour of the windshield.
Another significant disadvantage of prior art wiper blade heating assemblies as described above involves the problems associated with premature aging of the wiper blade caused by thermal abrasions and fatigue to the body of the blade as a result of localized high heat output temperatures against the wiper blade in direct contact with the heating element. This form of direct heat contact with a high heat output generated by prior art heating elements, typically results in the loss of elasticity in the rubber material comprising the wiper blade. In this regard, the heat output of prior art heating elements generally promotes degradation in the elastomeric characteristics of the rubber of the wiper blade, thus facilitating a shorter life span for the blade.
To counter these disadvantages associated with premature aging and thermal fatigue of wiper blades of prior art heating assemblies, those skilled in the art introduced various types of lubricants and parting agents to minimize the frictional and heat-induced effects caused by direct contact between the heating element and the wiper blade. Maintenance of lubricants or parting agents, however, generally presents multiple problems because of the difficulty in ascertaining whether the lubricant has been evaporated, or not, by the heat output of the prior art heating elements.
In addition, wiper blade heating assemblies of the prior art typically require complex assembly configurations which are neither easily replaceable or adaptable to conventional wiper blades or wiper assembly arms. For example, prior art weather protective hoods were developed by those skilled in the art which are made of a thin, rubber-like material which encloses and seals a pressure distributing wiper frame.
While the prior art wiper blade heating assemblies disclosed above may appear generally suitable for their intended purposes, these prior art heating assemblies nevertheless leave much to be desired from the standpoint of manufacturing costs, simplicity of construction and effectiveness of operation.